A typical data storage system includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute. Digital information, representing various types of data, is typically written to and read from the data storage disks by one or more transducers, or read/write heads, which are mounted to an actuator and passed over the surface of the rapidly rotating disks.
The actuator typically includes a plurality of outwardly extending arms onto which an air bearing slider is mounted at the extreme end of the arms. One or more transducers, in turn, are mounted on the slider. Airflow produced above and below the respective surfaces of the rapidly rotating disks results in the production of an air bearing upon which the aerodynamic slider is supported, thus causing the slider to fly a short distance above the rotating disk surface.
The actuator arms are interleaved into and out of the stack of rotating disks, typically by means of a coil assembly mounted to the actuator. The coil assembly generally interacts with a permanent magnet structure, and the application of current to the coil in one polarity causes the actuator arms and sliders to shift in one direction, while current of the opposite polarity shifts the actuator arms and sliders in an opposite direction.
In a typical digital data storage system, digital data is stored in the form of magnetic transitions on a series of concentric, closely spaced tracks comprising the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a plurality of sectors, with each sector comprising a number of information fields. One of the information fields is typically designated for storing data, while other fields contain sector identification and synchronization information, for example. Data is transferred to, and retrieved from, specified track and sector locations by the transducers being shifted from track to track, typically under the control of a controller. The transducer assembly typically includes a read element and a write element. Other transducer assembly configurations incorporate a single transducer element used to read and write data to and from the disks.
Writing data to a data storage disk generally involves passing a current through the write element of the transducer assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the transducer assembly sensing the magnetic field, or flux lines, emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface results in the production of an electrical signal, often termed a readback signal, in the read element.
A trend has developed in the data storage system manufacturing community to miniaturize the chassis or housing of a data storage system to a size suitable for incorporation into miniature personal computers, such as lap-top and pocket-sized computers, for example. Various industry standards have emerged that specify the external housing dimensions of small and very small form factor data storage systems. One such recognized family of industry standards is the PCMCIA (Personal Computer Memory Card Industry Association) family of standards, which specifies both the dimensions for the data storage system housing and the protocol for communicating control and data signals between the data storage system and a host computer system coupled thereto.
Recently, four families or types of PCMCIA device specifications have emerged. By way of example, a Type-I PCMCIA data storage system must be fully contained within a housing having a maximum height dimension of 3.3 millimeters (mm). By way of further example, a Type-II PCMCIA device housing must not exceed a maximum height of 5.0 mm in accordance with the PCMCIA specification. A maximum height of 10.5 mm is specified for the housing of Type-III PCMCIA devices, and Type-IV devices are characterized as having a maximum housing height dimension in excess of 10.5 mm. It is anticipated that the industry trend of continued miniaturization of data storage systems will eventually result in the production of systems complying with the Type-II PCMCIA specification. Such Type-II PCMCIA data storage systems will likely have external housing dimensions of approximately 54 mm.times.86 mm.times.5 mm, and include a data storage disk having a diameter of approximately 45 mm and a width dimension similar to that of a standard credit card.
Reducing the size of a data storage system housing without sacrificing storage capacity is typically achieved by increasing the track density, or number of tracks-per-inch (TPI), of the data storage disk. It is generally desirable to reduce the separation distance between the slider/transducer assembly and the rotating data storage disk in order to increase the readback signal sensitivity of the transducer to the typically weaker magnetic transitions associated with higher density disks. When decreasing the transducer-to-disk separation distance, however, the probability of detrimental contact between the sensitive transducer and an obstruction on the disk surface significantly increases.
A prevalent surface irregularity that afflicts an appreciable percentage of conventional data storage disks is generally referred to as a thermal asperity. Thermal asperities are isolated submicron-sized particles, typically comprising silicon carbide material, that are embedded in the disk substrate. Such thermal asperities are often large enough to interfere with the flight path of a typical slider/transducer assembly by impacting with the slider/transducer assembly at a very high velocity. Further, thermal asperities arising on the surface of a data storage disk are generally distributed in a highly random manner, and change in shape and size in response to changes in disk and ambient temperatures. A collision between a transducer and a thermal asperity often renders previously written data unreadable or unrecoverable, and typically results in a hard read error condition.
Magneto-resistive transducers are particularly susceptible to interference from contact with thermal asperities. It is well-known that magneto-resistive transducer elements are very sensitive to variations in temperature, and are frequently used as temperature sensors in other applications. A collision between a magneto-resistive transducer element and a thermal asperity results in the production of heat, and a corresponding rise in transducer element temperature. Such transient temperature deviations are typically associated with an inability of the magneto-resistive transducer element to read previously written data at the affected disk surface location, thereby rendering the stored information unrecoverable.
Many attempts have been made to determine the source of thermal asperities. No single mechanism has yet to be identified, and it is believed that thermal asperity defects arise from numerous sources. Moreover, conventional disk-level or system-level screening tests have proven to be ineffective in adequately detecting the presence of thermal asperities. A known technique for protecting a transducer against collision with a disk surface obstruction, as disclosed in U.S. Pat. No. 5,157,568, involves recessing the transducer into a cavity provided on the slider. This suggested solution increases the transducer-to-disk separation distance, reduces transducer readback signal sensitivity, and severely limits the degree to which disk recording densities can be increased. Another known technique, such as that disclosed in U.S. Pat. No. 4,669,011, involves the use of elaborate disk obstruction sensing and avoidance apparatus and electronics. This solution, however, increases the mass of the slider body, the complexity of the data channel electronics, and the overall cost of the data storage system.
There exists in the data storage system manufacturing industry a keenly felt need to provide a simple, effective, and low-cost solution for protecting a transducer element against collisions with randomly distributed thermal asperities and other disk surface irregularities. There exists a further need to provide such a solution that requires only minor modification to the existing configuration of the air bearing slider. The present invention fulfills these and other needs.